Aerodynamic drag accounts for over 50% of a tractor trailer truck's total fuel consumption at highway speeds above 55 mph. A gap exits between the tractor and trailer which tends to trap air, creating a low-pressure wake behind the tractor, resulting in a net pressure difference and, therefore, creating drag. The gap distance between the tractor-trailer combination is dependent on the position of what is known in the art as a fifth wheel. The fifth wheel is a bearing, which serves as a coupling between the tractor and trailer. The position of the fifth wheel is adjusted to accommodate different weight distributions based on the load of the trailer. The gap distance typically varies from about 36 to 48 inches. The drag coefficient of the vehicle is dependent on the gap distance. More specifically, the larger the gap distance, the larger the drag coefficient, and conversely, the smaller the gap distance, the smaller the drag coefficient.
The gap causes the formation of a turbulent air mass creating a low-pressure wake behind the tractor, decreasing the fuel efficiency of the vehicle. The goal in aerodynamic design is to produce shapes that delay air separation. Maximum efficiency is achieved when airflow remains attached and moves parallel to the side of the vehicle such that air separation from the tractor is reduced and a constant and smooth airflow along the side of the vehicle is achieved.
One solution to reduce the gap distance has been to use fixed cab extenders to reduce the effect of unwanted drag. The fixed cab extenders are planar members which extend aft longitudinally from a back end of the tractor substantially parallel with the sides of the tractor. Ideally, the fixed cab extenders would extend across the entire gap between the tractor and trailer, which, as stated above, typically varies from 36 to 48 inches, to obtain maximum aerodynamic efficiency. However, if the fixed cab extenders were configured as described, as the tractor turned relative to the trailer, the trailer would impact and damage the fixed cab extenders.
Therefore, previously developed fixed cab extenders are positioned to have a large clearance space between a vertical trailing edge of the fixed cab extender and a front end of the trailer. This clearance space is required to prevent the front end of the trailer from impacting the fixed cab extenders during sharp, typically slow speed turns. Thus, there exists a need for a cab extender that may be selectively deployed within the clearance space between the tractor and trailer at high speeds to improve fuel economy, and retracted at low speeds to allow the tractor trailer truck to maneuver. Further, there exists a need for a cab extender that is adjustable in length to accommodate the variability in spacing encountered between the tractor and trailer.
One previously developed attempt at fulfilling some of these needs is disclosed in U.S. Pat. No. 3,711,146 issued to Madzsar (hereinafter “Madzsar”). Although the cab extender assembly disclosed in Madzsar may be somewhat effective, it is not without its problems. For instance, Madzsar teaches adjusting the length of the cab extenders based upon a sensed amount of articulation between a tractor and trailer and not based upon a speed of the vehicle. Therefore, the system of Madzsar lags behind actual conditions. More specifically, the cab extenders are not retracted until after the tractor and trailer are articulated, thus the potential exists that the cab extenders will not be retracted in time to prevent damage to the cab extenders, especially during emergency maneuvers. Thus, there exists a need for a cab extender assembly wherein the cab extenders are retracted prior to the act of articulation to impede damage to the cab extenders. Further, the cab extenders of Madzsar are not positionable into both a stowed position and a deployed position since Madzsar does not teach placing the cab extenders into a stowed position. Thus, access to the fifth wheel and accessories located between the tractor and trailer is impeded. Further, the fully retracted length of the cab extenders must be unduly short to permit full articulation of tractor relative to the trailer.